Staurotheca

ÁLVARO L. PEÑA CANTERO, 2017, Benthic hydroids (Cnidaria, Hydrozoa) from the Ross Sea (Antarctica) collected by the New Zealand Antarctic expedition BioRoss 2004 with RV Tangaroa, Zootaxa 4293 (1), pp. 1-65 : 36

Staurotheca sp.

( Fig. 11 F–I)

Material examined. Stn 53, palmate colony 85 mm high, basibiont of Hebella plana , and colony fragment 22 mm long (NIWA 117545); Stn 67, one colony 45 mm high (MNCN 2.03/617).

Description. Colonies palmate, up to 85 mm high and basally polysiphonic, with closely-knit mesh appearance due to frequent branching and anastomoses.

Hydrothecae arranged in decussate verticils of three, resulting in six longitudinal rows of hydrothecae; few basal branches with decussate pairs. Hydrotheca ( Fig. 11 F–I) immersed into branch in about half, or even less, of its volume. Adcauline hydrothecal wall with significant free portion ( Fig. 11 G). Abcauline wall straight or slightly convex basally, but concave distally ( Fig. 11 G, I). Hydrotheca cylindrical in lateral view ( Fig. 11 I), directed outwards at distal part. Hydrothecal aperture circular, directed downwards. Hydrotheca with mushroom-shaped diaphragm.

Measurements (in µm). Hydrothecae: abcauline wall 600–620, free part of adcauline wall 30–120, adnate part of adcauline wall 750, adcauline wall 690–780, diameter at aperture 210–220, maximum diameter ca. 320, diameter at diaphragm ca. 280. Cnidome: larger microbasic mastigophores 20–21 x 4.5, smaller microbasic mastigophores 9 x 3.

Remarks. The material studied is morphologically close to S. glomulosa by the general shape and size of the hydrotheca. However, they differ because the hydrothecae are arranged in decussate pairs in S. glomulosa . It also differs from S. dichotoma by the distinctly smaller diameter of the hydrotheca (e.g., the diameter of the hydrothecal aperture is 273–332 µm in S. dichotoma , cf. Peña Cantero et al. 1997a). It could be conspecific with the species described as Dictyocladium fuscum by Hickson & Gravely (1907), with which it agrees in the general shape and size of the hydrotheca and in the presence of decussate verticils of three hydrothecae. However, it would be necessary to examine the type material of that species before reaching a conclusion.

Ecology and distribution. The material was collected at depths between 197 and 286 m, off Cape Hallett.

Figures

FIGURE 11. Staurotheca pachyclada (Jäderholm, 1904): A – B, hydrothecae. Staurotheca polarsterni Peña Cantero, Svoboda & Vervoort, 1997: C – E, hydrothecae. Staurotheca sp.: F – I hydrothecae. (A from Stn 124; B from Stn 17; C – E from Stn 19; F – H from Stn 53; I from Stn 67). Scale bar: 250 µm.